Klusener, 37, is the club's highest scorer in the County Championship with 1,095 runs at an average of 78.

But he is leaving because the club wants to boost the number of England-qualified players in the first team.

The departure of off-spinner Brown will also help create opportunities for the club's younger talent.

"Northants have consistently stated a desire to increase the number of England qualified players beyond this season and especially provide real opportunity for the talent that the Northants Academy is producing," said chief executive Mark Tagg.

A veteran of 49 Tests and 171 one-day internationals for South Africa, and Player of the Tournament at the 1999 World Cup, Klusener joined Northants before the start of the 2006 season, having had previous spells in county cricket with Middlesex and Nottinghamshire.

He has scored over 1,000 runs in each of his three seasons at the County ground, and Tagg paid tribute to his "determination and application for the team".

But he added: "The club, however, has to look forward to the future and with the game going through significant changes over the next couple of years it is important that Northants is positioned to play a full role both developing talent for the county and hopefully full international duty."

Brown has taken almost 600 wickets for Northants in all competitions since making his first-team debut in 1996.

He was selected for England's 2001 tour to Sri Lanka, but only played in one warm-up game and was never given another chance.

Two years later, however, he enjoyed his best season for Northants, taking 66 wickets at an average of 23.71.

"This was a difficult decision for the club to make given Jason's commitment and dedication over many years," said Tagg.

"It was felt that this was the right time for both parties and gives Jason an opportunity of potentially continuing his career elsewhere while enabling younger players to develop at Northants."

The decision to release the pair follows recent announcements that Richard Logan and Richard Browning would also be leaving the club.